U Value Timber frame .15 or .21

marie15

Hi,
I'm looking at 3 timber frame quotes that I have and I'm wondering if there is much difference between a U Value of .15 or .21?

I know that .15 is a better U value but is it much better in terms of the financial investment?

Are there other differences that I need to keep an eye on when trying to decide between different companies?

Thanks a million :-)

dubrov

Both are very good and you are unlikely to notice much difference.

You can work out the heat loss difference by using the formula Q=UxAxdT

Where Q is the hear transfer in Watts, U is the U Value, A is the area of the timber frame and dT is the difference in temperature inside and outside the material.

I assume the difference in cost is double-digit thousands. It would take a very long time to earn that back with an improvement of just 0.06 U value.

The chances are you would be better off spending the money elsewhere (e.g. windows, heat pump).
You really need to think of the energy specification of the build as a whole to see where best to spend the money available.

BryanF

the max elemental u-value is 2.1w/m2k (TGD L)

I’d recommend where possible to improve on the minimum regulations

Has your provisional BER been carried out?

Dudda

I always put in as much insulation as I can afford. Usually with timeframe the 0.21 uvalue is a single stud filled with cellulose and the 0.15 is a twin wall stud also filled with cellulose. The twin wall is much better for sound in addition to heat retention. This requires a lot more timber as its twin wall and a lot more expensive as a result. See if you can get a quote for a single stud filled with cellulose with an additional 50mm pir insulation internally as that would be cheaper and a good compromise.

BryanF

Dudda wrote: »

I always put in as much insulation as I can afford. Usually with timeframe the 0.21 uvalue is a single stud filled with cellulose and the 0.15 is a twin wall stud also filled with cellulose. The twin wall is much better for sound in addition to heat retention. This requires a lot more timber as its twin wall and a lot more expensive as a result. See if you can get a quote for a single stud filled with cellulose with an additional 50mm pir insulation internally as that would be cheaper and a good compromise.

twin wall would be my preference: decrement delay and beneath of service cavity for wiring/plumbing/lights/speakers etc is better than drylining PIR boards IMO, You could still use rock wool or PIR around reveals in the service cavity zone.

Dudda

BryanF wrote: »

twin wall would be my preference: decrement delay and beneath of service cavity for wiring/plumbing/lights/speakers etc is better than drylining PIR boards IMO, You could still use rock wool or PIR around reveals in the service cavity zone.

I'd be all for twin wall too but it's a major cost issue which needs to be considered. It's usually several thousand more. What I meant with PIR boards was they'd be fixed to the studs internally, then VCL and then the batten over through the insulation into the studs to create the service void and then plasterboard. No drylining PIR boards. The advantage this has is it reduces the tiny cold bridge through the single studs, low u-value and less timber so lest cost.

Another option is if the solid studs (which are usually 200 or 225mm deep) are replaced by JJI studwork which are 300mm deep you'll get 300mm of pumped cellulose. This could be the best cost wise as you've only one type of insulation to fit.

sydthebeat

Dudda wrote: »

I'd be all for twin wall too but it's a major cost issue which needs to be considered. It's usually several thousand more. .

are you building in Rep of Ireland?

Have you had a preliminary DEAP assessment carried out?
if you have, you should know its not simply a choice of upgrade or not.

marie15

Hi,

Thanks very much for your replies, I think I need to sit across from my Engineer/DEAP Assessment professional and see what is the best option for me all things considered.

Having spent a long time looking through the quotes and the component schedules, I have to come to the conclusion that I just don't have the knowledge myself to make a call on it.

Thanks again :-)

BryanF

Dudda wrote: »

I'd be all for twin wall too but it's a major cost issue which needs to be considered. It's usually several thousand more. What I meant with PIR boards was they'd be fixed to the studs internally, then VCL and then the batten over through the insulation into the studs to create the service void and then plasterboard. No drylining PIR boards. The advantage this has is it reduces the tiny cold bridge through the single studs, low u-value and less timber so lest cost.

Another option is if the solid studs (which are usually 200 or 225mm deep) are replaced by JJI studwork which are 300mm deep you'll get 300mm of pumped cellulose. This could be the best cost wise as you've only one type of insulation to fit.

The twin wall can be a cheap material route in comparison to 225’s or the I-joist types. IMO the twin wall as it easy to work with